The present invention relates to engine control system and method which are designed to utilize a speed density system for calculating the quantity of intake air in the combustion chamber of an internal combustion engine on the basis of pressure data in the intake manifold of the internal combustion engine.
The control system of the conventional internal combustion engine is so constructed that many operation data of the engine are gathered by many sensors for calculating predetermined control values in response to the operation data with a suitable calculating means so that many actuators are driven by output signals responsive to the calculated control values to enable many mechanisms to be controllably driven in response to the predetermined control values.
In the conventional internal combustion engine, the quantity of intake air (A/N) to be supplied to the combustion chamber is adjusted in response to the opening of a throttle valve, and the quantity of fuel corresponding to the quantity of intake air in response to the opening of the throttle valve and the revolution of the engine is supplied to the combustion chamber of the engine.
There has been well known in the art a typical engine which employs "a speed density system" for calculating intake air quantity data for use in a fuel supply mechanism and advanced angle quantity data for use in ignition timing control on the basis of pressure levels of air in the intake manifold. The speed density system is advantageous in that a pressure sensor is provided in an air duct held in communication with the intake manifold to sense pressure levels of air in the intake manifold by way of the air duct instead of an airflow sensor provided in the intake manifold to directly sense the quantity of intake air in the intake manifold, resulting in reducing the intake air resistance of the intake manifold and, thus, in decreasing costs of the sensors.
On the other hand, the internal combustion engine having such a speed density system is operated in such a manner that the intake air quantity is calculated in response to the vacuum pressure of air to be introduced into the intake manifold. In such an internal combustion engine wherein intake-exhaust mechanisms such as, for example, timing cams are exchanged while the cylinder operation modes are varied with the cylinders fully and partially operated, the relationship between the intake air pressure and the intake air quantity is fluctuated, thereby making it impossible to ensure desirable and adequate intake air quantity to be introduced into the cylinders of the engine.